1. Field of the Invention
The present invention relates to a power supply apparatus having a conductive case which houses electric and magnetic components.
2. Description of Related Art
An electric vehicle or a hybrid vehicle is provided with a power supply apparatus for a DC-DC converter or the like, which has a case housing electric components constituting a power supply circuit. For example, refer to Japanese Patent Application Laid-open No. H11-299220. The case is constituted of a conductive case body and a conductive case lid for electromagnetic shielding. Accordingly, this case prevents electromagnetic noise emitted from magnetic components such as a transformer or choke coil from leaking outside the case. This makes it possible to prevent electric components or electronic devices present in the vicinity of the power supply apparatus from being affected by the electromagnetic noise.
The reason is that, although a magnetic flux perpendicular to the bottom or case lid of the case is generated when the magnetic component is energized, since eddy currents flow in the inner surface of the case in a direction to cancel out the magnetic flux, the magnetic flux can be prevented from leaking outside the case.
However, since the case is constituted of a combination of the case body and the case lid, the eddy currents cannot flow from the case lid to the case body and vice versa sufficiently, if the conductivity at the joint surface between them is not high sufficiently. For example, if a gap or an oxide film is present in the joint surface, the conductivity of the joint surface is degraded. In this case, the eddy currents may leak from the inside surface to the outside surface of the case body or the case lid through the joint surface, causing electromagnetic noise to leak outside the case. Further, if the contact pressure at the joint surface is small, and accordingly, the contact resistance is large, a similar problem may occur. On the other hand, it is unfeasible to make the contact resistance sufficiently small throughout the circumference of the joint surface in view of the productivity and heat radiation performance of the case.